The MmpS family (mycobacterial membrane protein small) includes over 100
small membrane proteins specific to the genus Mycobacterium that have
not yet been studied experimentally. The genes encoding MmpS proteins
are often associated with mmpL genes, which are homologous to the RND
(resistance nodulation cell division) genes of Gram-negative bacteria
that encode proteins functioning as multidrug efflux system. Deshayes et al. (2010) showed
by molecular genetics and biochemical analysis that MmpS4 in
Mycobacterium smegmatis is required for the production and export of
large amounts of cell surface glycolipids, but is dispensable for
biosynthesis per se. MmpS4 is dispensable for transport to the
surface. Orthologous complementation demonstrated that the MmpS4
proteins are exchangeable, thus not specific to a defined lipid species.
MmpS4 function requires the formation of a protein complex at the pole
of the bacillus, which requires the extracytosolic C-terminal domain of
MmpS4. Deshayes et al. (2010) suggested that MmpS proteins facilitate lipid biosynthesis by
acting as a scaffold for coupled biosynthesis and transport machinery.